Why Some People Can Eat Whatever They Want and Not Gain Weight

Why Some People Can Eat Whatever They Want and Not Gain Weight

We all know the kind of people the reader is talking about - the "irritating" people who can finish two to three servings, eat bags of junk food all day, and not gain a pound. I say "irritating" because the rest of us have to watch what we eat and exercise regularly or we start developing rolls of unwanted fat. I remember shaking my head in amazement (and, okay, I'll admit, quite a bit of envy) as my stick-thin high school classmates would merrily eat whatever they wanted. I wondered what magic ingredient their bodies contained. It was obvious that there was a distinct difference in the way they burned their calories compared to the way I did.

Looking at it from the other side of the fence, there are many readers who tell me how frustrated they are that they cannot gain weight. They also want to know why their bodies are this way.

Therefore, whether you are a person who is struggling to lose weight or a person who is striving to gain weight, this topic might be of interest to you since the factors that affect the way we burn calories are really just two sides of the same coin.

Genetic factors.

A famous landmark study by Dr. Claude Bouchard in 1990 involving twins showed that weight gain appears to be influenced by genetic factors. Twelve pairs of lean young male twins were fed 1,000 extra calories for 100 days. Theoretically, they should have all gained the same amount of weight - approximately 29 pounds since it takes 3,500 extra calories to make one pound of fat. Instead, each twin pair gained almost exactly the same weight in the same place (upper bodies, abdomen, legs, etc.) but there was a 91/2 to 29-pound difference between the twelve pairs.

Metabolism and body composition.

Your body lives on the energy (measured in terms of calories) from the food you eat. The rate or speed at which you burn these calories is called metabolism. Your body needs a certain amount of calories for 'general housekeeping duties' such as breathing, heart pumping, cell repair, etc. This is called your resting metabolic rate or RMR. You burn these calories even if you are just lying still for twenty-four hours.

Dr. Eric Ravussin, Ph.D. and his associate, Dr. Pietro Tataranni, are experts in the field of metabolism. Dr. Ravussin put people inside a 'calorie-measuring' room that measured how many calories people consumed by analyzing their breath. The room contained motion detectors to monitor how much movement they made. Ravussin discovered that the tendency to have a slow or fast metabolism runs in families. Members of the same family tended to have the same metabolic rate.

Ravussin also measured the RMR of people by making them lie down for 40 minutes without moving. He found that people with the same weight, height and body shape can burn different amounts of energy each day. He found ranges of 1,067 to 3,015 calories per day.

What accounts for such a wide range of difference? One explanation is body composition. Your body can be divided into 'fat mass' and 'lean body mass' (also called 'fat-free mass'). Lean mass is everything in your body that is not fat - muscle, bones, blood, organs, skin, hair, teeth, etc. Lean mass is highly metabolic meaning it requires many calories to maintain itself. Your internal organs like your brain, kidneys and liver are working non-stop and need fuel to keep going. Muscles, including the heart, are also 'calorie-hungry'. People with a higher lean body mass or more muscle mass will have a faster metabolic rate. Researchers at Tufts University in Boston have found a significant similarity in lean body mass, especially muscle, in members of the same families implying that there is a genetic component involved.

The "fidget" factor.

In the calorie-measuring room experiment, Ravussin discovered that people have different 'fidget' levels. Fidgeting is spontaneous physical activity or movement made without thinking. Examples of fidgeting are twirling your hair as you talk on the telephone or jiggling your leg as you work at your desk. He discovered there is a big difference in the way people perform an everyday activity like watching TV. Some people sat as still as statues without moving a muscle. Others couldn't stop from changing position every so often. Others kept getting up and moving around the room. Ravussin calculated that fidgeting alone could burn anywhere from 300 to 800 calories a day. He found that the tendency to fidget or to be restless also ran in families.

Nervous energy.

We are talking here about the high-strung, "hyper", tense or nervous person. The one who makes you nervous just being around him or her. Ravussin theorized that since nerves control things like muscle tension, breathing, heart rate, etc., people whose nerves are running at a higher level than everyone else's will burn more calories even when they are forced to lie still.

In the Mayo Clinic in Minnesota, researchers James Lavin and Norman Eberhardt fed 16 normal weight men and women an extra 1000 calories for two months. The participants refrained from exercising. The weight gain ranged from 2 to 16 pounds. The researchers found that the ones who were the most nervous and "hyper" gained the least.

Body heat.

Another explanation for calories that just seem to vanish into thin air is called "facultative thermogenesis" or heat production not related to resting metabolic rate. It seems that some people are "efficient" (from a survival standpoint) calorie burners and store most excess calories as fat or fuel for the future. Others are "inefficient" calorie burners and "waste" the excess calories as body heat. No one can fully explain the mechanism behind this. Some think it is related to the "brown fat theory". Brown fat is a special kind of fat that helps regulate body temperature. How much brown fat you have depends again on your genes. Judith Wurtman of the Massachusetts Institute of Technology found that the more obese the person, the less active the brown fat cells were. However, she also noted that exercise increases brown fat activity.

A related theory is that heat is always escaping from the core of your body through your skin out to the environment. People who are tall, lean and lanky have more skin surface area than people who are short and stocky and, thus, burn more calories because more heat is escaping through their skin.

Junk food and no exercise a poor lifestyle.

Just being thin does not equal healthy and fit. Eating junk food and not exercising can cause a thin person to fall prey to the same diseases (hypertension, heart disease, stroke, etc.) as obese people who follow the same lifestyle.

Besides, as people age, metabolism slows down (primarily because of muscle atrophy and lack of exercise), so thin people who never developed good eating and exercise habits in their youth end up (surprise, surprise!) overweight. I discovered this in my 25th high school reunion this year. Many of my once thin classmates were overweight while I, who struggled with my weight all through high school, was now the slim one.